1. Field of the Invention
The present invention relates to a roving machine including a wind-up speed changing apparatus, which reduces a bobbin rotational speed in response to the increased number of roving layers wound onto the bobbin.
2. Description of the Prior Art
In roving machines of bobbin loading type, a sliver let out of a front roller at a certain speed is wound up over a bobbin while twisting the sliver due to a difference in rotational speed between a flyer rotating at a predetermined speed and the bobbin rotating at a higher speed. The bobbin is supported by a bobbin rail and vertically moved therewith. Each time the direction of up/down movement of the bobbin rail is changed, the distance through which the bobbin rail moves is shortened to wind up the sliver so that the wound thread (roving) roll has a conical shape at both ends.
To satisfactorily wind up a sliver, the winding is required to be performed under such a condition that there is a proper slack in the sliver between the front roller and a flyer top. If a tension of the sliver is fluctuated during the winding, the weight of the wound roving per unit length is also fluctuated to make the roving uneven. Also, to hold the sliver tension constant for proper winding, the winding must be performed so that the let-out amount and the wind-up amount of the sliver becomes almost equal to each other during the winding; otherwise unevenness and disconnection of the roving may occur due to fluctuations in the sliver tension.
When the bobbin rotational speed is kept constant from start to end of the winding, the wind-up speed increases with an increase in the number of wound roving layers (i.e., the diameter of the wound roving roll). Therefore, a speed changing apparatus using a pair of cone drum and belt shifter has been conventionally employed to control the bobbin rotational speed to be gradually lowered as the number of roving layers wound around the bobbin increases.
However, because the rate of increase of the roving roll diameter with respect to the number of roving layers wound around the bobbin is changed depending on the roving conditions, it has been required to change the configuration of the cone drum (or replace the cone drum) depending on the roving conditions, or modify the amount of movement of the belt shifter by using an adjustable auxiliary cam depending on the roving conditions (see Japanese Patent Publication No. 52-48652). Thus, a troublesome replacement or adjustment operation has been required for each change of the roving conditions.
To solve those disadvantages, there has been proposed and practiced an apparatus in which a sensor is provided between the front roller and the flyer top for detecting the position of the sliver leading from the front roller to the flyer top, and a belt trained over a cone drum is shifted to adjust the bobbin rotational speed so that the position of the sliver under roving is kept at a preset target position, thereby controlling the winding tension (see, for example, Japanese Patent Laid-Open No. 62-85304).
There has also been proposed an apparatus in which a gear system for driving a long rack in cooperation with the belt shifter is driven by a motor, and driving of the motor is controlled so that an amount of movement of the belt shifter becomes a value corresponding to the number of wound roving layers and input in a microcomputer beforehand (see Japanese Patent Laid-Open No. 62-117829).
Further, there has recently existed a keen demand for multikind and small-quantity production. To accommodate frequent changes of the roving conditions encountered in such production, a roving machine has been proposed in which a sliver drive system and a winding drive system are separately operated by respective variable speed motors, and driving of these variable speed motors is controlled based on data input to a storage beforehand depending on the roving conditions (see, for example, Japanese Patent Laid-Open No. 63-264923).
In the apparatus disclosed in Japanese Patent Publication No. 52-48652 that the amount of movement of the belt shifter is adjustable, while replacing the cone drum is not required upon each change of the roving conditions, it is necessary to set a proper amount of movement of the belt shifter upon each change of the roving conditions in order that the amount of decrease in the bobbin rotational speed becomes an appropriate value corresponding to the increase in the number of wound roving layers.
Also, in the apparatus disclosed in Japanese Patent Laid-Open No. 62-17829 in which a sliver drive system and a winding drive system are separately operated by respective variable speed motors, it is necessary, upon each change of the roving conditions, to set a proper amount of decrease in the bobbin rotational speed corresponding to an increase in the number of wound roving layers.
For setting a proper amount of movement of the belt shifter for a proper amount of decrease in the bobbin rotational speed, if there are data obtained in the past from a sliver carried out under the same conditions, those data can be used. If not, the setting must be made through estimation only based on past experiences and intuition of an operator. However, since the resulting estimated value is not always a proper value, trial roving is needed.
Depending on the roving conditions, the trial roving must be often repeated several times until the estimated value approaches the proper value. This gives rise to problems in that raw materials and labor necessary for the trial roving are wasted and the operating ratio of the roving machine is lowered. These problems become severer with frequent changes of the roving conditions to be adapted for multikind and small-quantity production.